Evaporator devices for volatile substances are very well-know, for diffusing air fresheners, pesticides or similar chemical substances.
Two basic types of such heating devices are manufactured: a first type in which heating of a support plate impregnated with the desired active ingredient is performed; and a second type in which a wick is provided, said wick being partially immersed in a small bottle containing said substances in liquid form and conveying, by means of capillarity, the essence into the vicinity of a heating element.
Evaporating devices with electrical heater to activate evaporation are known for many years. Many of them present the advantage of having regulation means in order to adjust the evaporation rate.
Most of these regulation means are dealing with mechanical constructions that affect the heat transfer from the heater to the wick:                by varying the position between wick and heater, see for example patents EP-0942648, EP-0962132.        by varying the air flow around the wick (chimney effect), see for example patents EP-1064957 and EP-1358891.        
In some other cases, electrical constructions are used to adjust the power dissipated in the heater, as described for example in the U.S. Pat. No. 6,661,967. In others, temperature of the wick can be adjusted by selectively activating several heaters placed around the wick, see for example European Patent EP-1247446B1.
However, each specific chemical active ingredient to be vaporised, and more specially perfumes, have an intrinsic working evaporating range temperature. For an optimum operation, regulation of the maximum and minimum temperature should be within this intrinsic working evaporating range of the particular chemical active ingredient to be evaporated.
In fact, regulation of the evaporation rate of perfume by changing applied heat is not a trivial question: due to the fact perfumes are very complex mixtures of a high number of different chemical components, each of them having its own volatility behaviour, any change of temperature will modify the composition of the vapours emanated. Thus the maximum-minimum range of regulation should be controlled in order to guarantee the evaporation conditions do not results in an unacceptable modification of the olfactory note of the perfume.
Current regulations means present the following drawbacks:
(i) For solutions where regulation is achieved through the mechanical construction, it is not possible to change the regulation range (meaning wick temperature and max and min value) without changing the mechanical construction of the device, which means that different designs or variants of the components of the device have to be manufactured, for which different moulds and manufacturing tools have to the produced for the different parts involved. The corresponding economic investment is generally not possible to assume.
Therefore, a particular evaporator device can only be used with a limited variety of perfume compositions, thus, it is the perfume chemical composition that has to be adapted to the regulation capabilities of the device and not the opposite.
(ii) For solutions where regulation is done by electrical means, the minimum and maximum temperature can be set to the correct value for each perfume by changing the ohmic value of electrical resistors used in the device. However, this kind of regulation only allow a limited number of values (2, max 3 according prior art). This lack of freedom for the consumer can lead to insatisfation as minimum performance can be too low and maximum too high, with no possibility for an intermediate value.
Therefore, there is no solution in the prior art providing gradual regulation between minimum and maximum evaporation rate, with the possibility of adjusting the regulation range of the same evaporator device (without modifying its physical design), for a wide variety of perfumes.